RE: Re: Reinforcement Pad Weep hole

The discussion seems to digressing from original points (i.e., the reason for such failure)

From a layman's perspective ( as I am), the reinf. pad is not supposed to hold pressure. I understand that when one creates an opening in vessel / piping for putting nozzles, to take care of the weakened shell around the opening, one puts reinf. pad (after due calculation or following some rule of thumb, as the case may be. . That is, the reinf. pad strengthens the shell.

The reinf. pad has one or two openings or weep holes, depending on the size of reinf. pad. The presence of holes helps in venting the air etc. between the pad plate & the shell (vessel / piping, as the case may be). The hole is also necessary if one does pneumatic testing to check the soundness of pad welding. After completion of the jobs, the holes are supposed to be blocked with 3/4" brass bolts ar something like that. They are never recommended to be closed permanently by, say, dropwelding etc. The basic argument, as some experts told me, is to allow venting of gases/vapours etc., just in case.

We had once faced similar failure from reinf. pad some 10+ yrs. back. A vessel was fabricated to meet some process modification need. (No, no certified ASME/API Inspector was involved - we do it ourselves). The vessel had 12" opening which had a reinf. pad too. The reinf. pad welding job was done overnight, with some breaks. That night, it did rain ( "In Assam, it never rains. It pours." - Goethe). On hidsight, it was felt, that rainwater ingress took place between shell and the pad. Additionally, someone closed the weep hole after completion of pad welding. It was an emergency job and all systems etc., were bypassed.

After commissioning the vessel, when the vessel reached about 320 C, the reinf. pad burst open. The shell was pushed internally by about 6" max. The reason attributed was - water convereted to steam at higher temp and created necessary bursting force. Again some expert told us that a pressure of around 3-4 kg/cm2 between shell and reinf. pad is good enough to do that.

Let me tell you - we were very happy at that time. The management did not bypassed us for any simple things for next three years.

'Hope it helps

Regards.

-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=W_4u1zzv-r97mBgdoX4E_GKkvYRNTX3R8-yNPdjdPzwdjQ9vxPUVxMLOpAJmYwW6panz5nTJtEe1aPhmHEDjCTNlqzc">PipingDesign@yahoogroups.com</a> [mailto:PipingDesign@yahoogroups.com]On Behalf Of tomcruz55 Sent: Wednesday, September 14, 2005 9:33 AM To: <a href="/group/PipingDesign/post?postID=W_4u1zzv-r97mBgdoX4E_GKkvYRNTX3R8-yNPdjdPzwdjQ9vxPUVxMLOpAJmYwW6panz5nTJtEe1aPhmHEDjCTNlqzc">PipingDesign@yahoogroups.com</a> Subject: [PipingDesign] Re: Reinforcement Pad Weep hole

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Received on Wed Sep 14 05:14:00 2005